What Is Cancer?

Key points about childhood cancer

• sometimes things can go wrong with the way cells divide and multiply and cancer can develop
• the aim of treatment for most childhood cancers is cure
• remission is a step on the road to cure but your child will usually need more treatment
• treatment may include a combination of chemotherapy, surgery, radiotherapy, immunotherapy, bone marrow or stem cell transplant
• treatment may take a few weeks, several months or even years
• relapse is the term used when, despite treatment, the cancer returns but a cure might still be possible

Normal cell growth

Every human body has millions of cells

The human body is made up of many millions of tiny building blocks called cells. Each organ of the body contains its own special type of cells. Each type of cell has a special function, for example:

• kidney cells get rid of waste products
• muscle cells move a joint

Inside a cell's nucleus

Every cell has a central part called the nucleus that contains the genetic material inherited from parents. It contains DNA, chromosomes and genes. 

The nucleus of every cell contains all the information needed to make a human being. A molecule called deoxyribonucleic acid (DNA) packages this information within the cell's 46 chromosomes. Genes within each chromosome give specific instructions to tell the cell how to operate.

Cells divide and multiply throughout life

The human embryo, before birth, has only a handful of cells. These cells divide and multiply in the small embryo. They gradually become more specialised over the pregnancy, forming more specific parts of the body such as bones or the heart. The process of cells dividing and multiplying continues after birth and throughout life. This process replaces old cells that have been damaged through wear or injury. Some cells, such as skin and bone marrow cells, can do this very quickly. Others, such as nerve and muscle cells, do this slowly.

The making of a human being is very complex and sometimes things can go wrong with this process.

How cancer develops in children

Cancer develops when a cell in the body starts to divide and multiply without normal controls. A mistake in the cancer cell's genes tells the cancer cell to grow, divide and multiply. Millions of cancer cells can grow from one cancer cell.

At first it may not be obvious but a build up of cancer cells may produce a tumour or lead to other symptoms.  

The most common types of childhood cancer

Cancer is not one disease, but more than a hundred different diseases. Each has its own pattern of behaviour, response to treatment and outcome. The most common types of childhood cancer are:

• leukaemia (cancer of the white blood cells)
• lymphoma (cancer of the lymphatic system)
• glioma and medulloblastoma (types of brain tumour)
• neuroblastoma (cancer of a type of nerve cell)
• rhabdomyosarcoma (tumour of muscle)
• osteosarcoma and Ewing's sarcoma (bone cancers)
• Wilms tumour (a type of kidney cancer)

Childhood cancers are rare. A new diagnosis of cancer happens in about 150 tamariki (children) in New Zealand each year. With few exceptions, there is no major risk of other tamariki in the same family developing the same cancer. A small percentage of cancers do run in families (for example, retinoblastoma).

Causes of childhood cancer 

The cause of cancer in tamariki is largely unknown. Everyone inherits important cell growth-controlling genes. These genes can either start or stop cell growth. Cancer may develop when a mistake happens and cells grow in an uncontrolled way. 

You can't catch cancer. There is no risk of one child passing the cancer on to another. There is no evidence that cancer happens following a knock or injury. Cancer does not develop because of something you did or didn't do - it's not your fault. 

The aim of treatment for childhood cancer

The aim of treatment for most childhood cancers is cure. There are still many unanswered questions about cancer. This can make it difficult to accurately predict the outcome for each child with cancer.

Treatment may include one or more of the following:

• chemotherapy
• surgery
• radiotherapy
• immunotherapy
• bone marrow or stem cell transplant

Treatment may take a few weeks, several months or even years.

Remission

Remission means that the cancer has responded to treatment and cancer cells are no longer seen, or they are at very low levels, on tests.  

This means the treatment has destroyed a large number of the cancer cells in the body. It is likely that there are still some cancer cells left that are too small to see in tests. Tests have become more accurate over time but no test can identify every cancer cell. Remission does not mean your child has been cured. It is a step on the road to cure. Your child will usually need more treatment over many weeks or months to destroy the remaining cancer cells.

There are different treatments for different types of childhood cancer. Your child's cancer team will explain your child's treatment and follow-up plans. 

A relapse

Relapse is the term used when, despite treatment, the cancer returns. During treatment and for a long time after the end of treatment, your child's cancer team will monitor your child for any signs of a relapse.

A relapse is frightening but a cure might still be possible. This depends on many things including the type of cancer. It is almost certain that your child will need a new or different treatment approach.